The present invention relates to doped polymeric films used as radiation hard, i.e., low radiation-induced conductivity, dielectrics.
The use of polymeric dielectrics is increasing in severe radiation environments such as those encountered in space, fusion and fission reactors, and weapon systems. Glass and ceramic insulators cannot replace polymeric materials in components requiring the mechanical flexibility or the low melting temperature of certain polymers. These components include cable-sheathing and "weaklink" capacitors which must short-out in fire accident environments for safety purposes.
In radiation environments, however, the radiation-induced conductivity (RIC) of polymeric dielectrics can render these materials useless for voltage hold-off and energy storage in capacitors, cables, and coatings. In such applications, it is often desirable that a polymer display the lowest possible RIC and retain superior dielectric properties such as high breakdown voltage, low current leakage, and the like.
Many excellent dielectric polymers have been patented for unique applications and operating environments. Thus, polyethylene terephthalate (PET) compositions containing various additives have been used in situations where fire retardance is desired (Dodson et al, U.S. Pat. No. 3,884,870; Akagi et al, U.S. Pat. No. 4,344,874; Hecht et al, U.S. Pat. No. 4,338,243). Other dielectric compositions, e.g., polytetramethylene terephthalate, as well as methods to improve dielectric properties of polymers in radiation-free environments have been disclosed (Smith et al, U.S. Pat. No. 4,000,109, and Betts et al, U.S. Pat. No. 4,209,566). PET chips have also been used in neutron radiation shielding (Blanco, U.S. Pat. No. 3,106,535).
It has also been disclosed that photo-conductive insulators such as certain epoxy resins can have their photoconductivity increased by doping with Lewis acids such as 2,4,7-trinitro-9-fluorenone (TNF) (Mammino, U.S. Pat. No. 3,408,184).
None of this art is concerned with the development of radiation hard polymer dielectrics with low radiation-induced conductivities.